BEHAVIOR 25 



6. The question of sensory cilia 



Certain of the body cilia behave differently from most. According 

 to Kahl (1935) the posterior cilia are strongly thigmotactic, 

 coming to a stop when they touch something substantial. Along 

 the ciliary rows it has been found that groups of cilia are stiff 

 and pointed outward while the remainder of the ciliation is actively 

 beating; and these have been called tactile spines, setae, or Tast- 

 borsten (Fig. 3). They may disappear and reappear. Hence Stein, 

 who seems to have first noticed them, thought they could be with- 

 drawn into the body. Johnson, with more probability, said that 



Fig. 3. Sessile body cilia as seen in S. roeseli, possibly sensory. 

 (After Kahl, 1935.) 



they were only temporarily rigid cilia which could start again 

 beating and only seemed longer than the others because they were 

 stopped. He suggested a sensory function for the cilia in the rigid 

 state because they are found mostly toward the anterior end where 

 stimuli would presumably be most frequent. Since Johnson saw 

 them both in coeruleus, which makes no case, and in roeseli which 

 does, they are not uniquely correlated with case building. He 

 found them most evident in the frontal view ; and Kahl states that 

 there is always one group of " bristles ", five to twenty in number 

 according to the species, in each kinety directly under the 

 membranellar band. 



